A steering wheel is a driver-manipulated element of a steering system of an automobile. Many studies have been conducted with regard to the steering wheel for improving its esthetic appearance, convenience of holding, use of functional elements therewith, etc.
In particular, when starting to drive an automobile in cold weather, the temperature of the steering wheel is lower than that of the human body, which affects the driver and might pose a safety problem.
Accordingly, various apparatuses for heating the steering wheel to a temperature greater than that of the human body have been studied.
In a conventional technique for heating a steering wheel as disclosed in Korean Utility Model Application No. 1989-0020599, Korean Patent Application No. 1992-0000945, and Korean Utility Model Application No. 1996-16958, heating coils 3 are buried in a rim 10 portion of a steering wheel structure as shown in FIG. 1.
In order to bury the heating coils 3, as shown in FIG. 2, an insulating covering material 2 is covered on an outer-side of the core 1 and the heating coils 3 are bonded to an outer circumference of the insulating covering material 2. Afterwards, a surface of the rim 10 is finished using a finishing member 4 such as a synthetic resin.
In another method of burying the heating coils 3, as disclosed in Korean Utility Model Registration Application No. 1996-066213 (FIG. 3), after winding a heating wire 5 in a coil shape on an outer circumference of the core 1, the surface of the heating wire 5 is finished by using a synthetic resin mold 6.
However, as shown in FIG. 2, when the heating coils 3 having a flat shape are covered and fixed on an outer circumference of the insulating covering material 2, placing the thin heating coils 3 with uniform distances between the thin heating coils 3 is quite difficult, and a temperature deviation between areas in the rim 10 is generated in practice due to the non-uniform distances between the heating coils 3.
Also, as shown in FIG. 3, when the heating wire 5 is wound in a coil shape, a temperature deviation can be generated due to the non-uniform winding gaps, and, in particular, since only a single heating wire 5 is wound, when the heating wire 5 breaks during a working process, it is necessary to replace and re-wind the entire heating wire 5 again.
Also, when the heating coil 3 or the heating wire 5 is buried as described above, it takes a certain period of time for the heat to transfer from the heating coil 3 or the heating wire 5 to a surface of the rim 10.
A plane heater 14 for a steering wheel is disclosed in Japanese Patent Laid-Open Application No. 2007-290685 (FIG. 4). In the plane heater 14, heating wires 17 are fixed on a supporter 16 of a non-woven material. FIG. 5 is a photograph of an actual plane heater 14, and FIG. 6 is a photograph showing a steering wheel including the plane heater 14. As shown in FIG. 6, the plane heater 14 is mounted on an outer circumference of a rim of the steering wheel.
The plane heater 14 provides a cushion comfort area when a driver holds the steering wheel since the supporter 16 of the plane heater 14 is formed of a non-woven material.
However, when the plane heater 14 is used, the thickness (diameter) of the steering wheel is increased due to a thickness of the supporter 16 made of a non-woven material. Also, the steering wheel is finished by covering an actual wood 20 or a leather to protect the plane heater 14 and to gentrify a decoration. In this case, the thickness of the steering wheel is further increased.
The Cubic Printing (Curl-fit) method for a rim of a steering wheel of a vehicle disclosed in Korean Patent Registration No. 10-0472399 of the current inventor cannot be applied to the plane heater 14 having a rough surface as described above. That is, a transfer film on which a wood pattern for an esthetic decoration of the steering wheel is printed cannot be directly transferred onto the rough surface of the plane heater 14. For a decoration of the steering wheel, as shown in FIG. 6, after processing a wood piece 20, the processed wood piece 20 must be applied to the plane heater 14 (after processing two pieces of woods having a semi-circle shape, the two pieces of woods are joined to surround the surface of the plane heater 14). In this case, the manufacture of the steering wheel is time-consuming, and thus, expensive. Also, due to the low thermal conductivity of the wood piece 20, the overall thermal conductivity of the steering wheel is low, and accordingly, the heat of the plane heater 14 cannot be efficiently utilized.